There's a big square "hole" in the sun this week, according to NASA's Solar Dynamics Observatory. The dark spot in the sun's outer atmosphere is a phenomenon known as a "coronal hole," a gap in the magnetic field where solar wind rushes out, reports Space.com. In the hole, which appears dark because there is less material emitting ultraviolet light, "you can see bright loops where the hot plasma outlines little pieces of the solar magnetic field sticking above the surface," NASA says.
But why is it square? "No particular reason," explains Mika McKinnon at io9. "Holes can be all sorts of shapes and sizes," she writes. "Given the variety of shapes and sizes, coronal holes make for a solar version of cloud-watching, identifying hidden shapes in the abstract patterns." Coronal holes can affect our planet's magnetic field if they are in the right position, but NASA says this one is so far south on the sun that it is unlikely to have any impact on Earth. (Read more NASA stories.)